The Long Term Evolution, “LTE”, standard uses Radio Network Temporary Identifiers or “RNTIs” to identify individual and/or groups of user equipments, “UEs”. A given UE may have multiple RNTIs active at any given time, e.g., for use in paging, random access, and uplink transmit power control.
In the case of uplink transmit power control, a network base station, referred to as an “eNodeB” in the LTE standard, sends Downlink Control Information or “DCI” messages that carry transmit power control, “TPC”, commands. For example, so called Format 3/3A messages are used to convey TPC commands for Physical Uplink Control Channel, “PUCCH”, transmissions by a UE, as well as TPC commands for Physical Uplink Shared Channel, “PUSCH”, transmissions by the UE. Different RNTIs are used to indicate whether the TPCs pertain to PUCCH or PUSCH power control.
Within this framework, the UE ties its transmit power control of uplink Sounding Reference Signal, “SRS”, transmissions to the TPC commands received for its PUSCH transmissions. In other words, LTE provides no mechanism for separately controlling the uplink transmit power of the SRS transmissions by a UE. Thus, SRS power control at the UE is made to depend on the network's closed-loop control of the UE's PUSCH transmit power, although the reception quality requirements and network reception points for PUSCH and SRS transmissions generally are different. These differences become particularly problematic in heterogeneous network environments where smaller cells, e.g., “pico” cells, associated with low-power access nodes overlay a larger, macro cell provided by an eNodeB or other relatively high-power access point.